1. Technical Field
The invention relates generally to wireless networks; and more particularly to interference reduction in cellular wireless data transmissions in such wireless networks to increase data handling capacity.
2. Related Art
Wireless networks are well known. Cellular wireless networks support wireless communication services in many populated areas of the world. Satellite wireless networks are known to support wireless communication services across most surface areas of the Earth. While wireless networks were initially constructed to service voice communications, they are now called upon to support data communications as well.
The demand for data communication services has exploded with the acceptance and widespread use of the Internet. While data services have historically been serviced via wired connections, wireless users are now demanding that their wireless units also support data communications. Many wireless subscribers now expect to be able to xe2x80x9csurfxe2x80x9d the Internet, access their email, and perform other data communication activities using their cellular phones, wireless personal data assistants, wirelessly linked notebook computers, and/or other wireless devices. The demand for wireless network data communications will only increase with time. Thus wireless networks are currently being created/modified to service these burgeoning data service demands.
Significant performance issues exist when using a wireless network to service data communications. Wireless networks were initially designed to service the well-defined requirements of voice communications. Generally speaking, voice communications require a sustained bandwidth with minimum signal-to-noise ratio (SNR) and continuity requirements. Data communications, on the other hand, have very different performance requirements. Data communications are typically bursty, discontinuous, and may require a relatively high bandwidth during their active portions. To understand the difficulties in servicing data communications within a wireless network, consider the structure and operation of a cellular wireless network.
Cellular wireless networks include a xe2x80x9cnetwork infrastructurexe2x80x9d that wirelessly communicates with user terminals/mobile stations within a respective service coverage area. The network infrastructure typically includes a plurality of base stations dispersed throughout the service coverage area, each of which supports wireless communications within a respective cell (or set of sectors). The base stations couple to base station controllers (BSCs), with each BSC serving a plurality of base stations. Each BSC couples to a mobile switching center (MSC). Each BSC also typically directly or indirectly couples to the Internet.
The wireless link between the base station and the USER TERMINAL is defined by one of a plurality of operating standards, e.g., AMPS, TDMA, CDMA, GSM, etc. These operating standards, as well as new 3G and 4G operating standards define the manner in which the wireless link may be allocated, setup, serviced and torn down. These operating standards must set forth operations that will be satisfactory in servicing both voice and data communications.
FIG. 1A illustrates a portion of a prior art cellular wireless network, and in particular a cell 100 of such a wireless network. As is shown, the cell 100 is subdivided into sectors 1, 2, and 3. The wireless network supports wireless communications within each of these sectors. In a typical installation, three separate transceiver units support the three separate sectors via three separate antennas. With this subdivision, user terminals 102, 108, 114, 116, and 118 are supported in sector 1. Further, user terminals 104, 110, 120, and 122 are supported in sector 2. Finally, user terminals 106, 112, 124, and 126 are supported in sector three. Both voice and data communications are supported within cell 100. In FIG. 1A, user terminals 102, 104, and 106 are voice units, while user terminals 108-126 are data units.
In operation, a user terminal, e.g., any of user terminals 102-126, communicates with a base station that supports the cell 100. A BSC coupled to the base station routes voice communications between the MSC and the serving base station. The MSC routes the voice communication to another MSC or to the PSTN. BSCs route data communications between a servicing base station and a packet data network that may include the Internet.
In the conventional multi-sector system of FIG. 1A, data is transmitted at any given time over all of the sectors, as is illustrated in FIG. 1B. However, the time continuum must be shared by all of the user terminals operating within each of the sectors. In a CDMA system, transmissions to different users within a sector are distinguished using Walsh coding wherein a single Walsh code, or plurality of Walsh codes is/are used to distinguish each user. Each sector has a separate pilot signal multiplexed with the data signal that is then transmitted from a sectorized antenna structure. A consequence of these simultaneous transmissions is inter-sector interference, especially with respect to mobiles located near the sector borders. Further, inter-cell interference occurs for users located at the boundaries of cells where users receive signals from two (or more) base stations. Users in those regions may receive weaker signals and receive higher interference. The higher interference adversely affects performance within the sector reducing the data rate that may be throughput upon the forward link.
Thus, there is a need in the art for a system and method of operating a cellular wireless system to increase data throughput capacity.
A system and method of the present invention employs a multi-beam per sector solution with interference avoidance to increase data handling within a cellular wireless network. As described herein, the present invention exploits packet data transmission characteristics and designs the transmission time interval and the basic slot structure of packet data transmissions such that the forward link packets transmitted among adjacent beams of a multi-beam per sector configuration are orthogonal in time.
The entire multi-beam configuration for a base station is arranged such that no adjacent beams, even across sector boundaries, are transmitting data on the forward link during the same time intervals. Thus, to achieve interference avoidance, the present invention involves synchronizing the packet transmission timing interval and scheduling packet transmission times such that adjacent beams do not transmit data during the same intervals.
Other features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not limitation. Many changes and modifications within the scope of the present invention may be made without departing from the spirit thereof, and the invention includes all such modifications.